The operation of chemical processes and the reactions involved therewith may generally result in the deposition of coke and growth of coke blooms on the internal surfaces of process equipment. The presence of coke increases the temperature of the internal surfaces which results in carburization and metal loss of the internal surfaces. For example, catalytic reforming reactions which involve the conversion of naphtha hydrocarbons to reformate may foul the internal surfaces of furnace tubes with coke including at least one or more of catalytic coke and thermal coke. These initial coke deposits may grow over time into coke blooms. The service life of the process equipment is negatively impacted by the carburization and metal loss which results from coke blooms.
Metal protective layers (for example a stannide layer) may protect the internal surface of the process equipment by inhibiting the rate of carburization and metal loss. However, the metal protective layer itself may become compromised due to erosion mechanisms from the processes, processes that are aggravated by high temperatures at localized regions where coke growths inhibit efficient heat transfer.
Even with a metal protective layer protecting the internal surfaces of the process equipment, the internal surfaces need to be periodically evaluated to assess the condition and service life of the process equipment. An example of such evaluation includes intelligent pigging using smart ultrasonic testing (UT gauging) and/or internal video inspection. However, the internal surfaces of the process equipment need to be decoked prior to this evaluation, since problem areas may be hidden by coke deposits, and evaluation without decoking results in incomplete data when using standard external UT gauging and results in semi-qualitative data when using internal video inspection.
Industrial decoking methods include steam decoking and hydraulic pig scraping, both of which damage the metal protective layer protecting the process equipment's internal surfaces. As an alternative, hydroblasting has been used to decoke the internal surfaces of process equipment having metal protective layers. However, hydroblasting is very time-consuming and is uneconomical in many cases due to required downtime of the process equipment.